(All statistics referenced are from https://www.mlb.com/.)
Now that most teams have played at least 30 games, we are about 1/5 of the way through the 162 games for each team, which still leaves a huge amount of baseball to be played. However, a lot of predictions and inferences can be made with this large sample size of April, and while they may not hold up, they do have solid evidence behind them. So with that, let's review the pennant races after April.
NL East
The NL East is shaping out to be a competitive division this year, not because all the teams are exceptionally good, but because the teams are well-matched (excluding the MLB-worst Marlins). The Phillies got off to a hot start but cooled off for a bit and picked up steam again, winning seven of their last 10 to lead the division by 1.5 games over the Braves, who are also heating up. The Mets and Nationals are under .500 and slowing down.
NL Central
This division has been wildly competitive as of late, and going to be in my opinion the most fun to watch over the next few weeks. The red-hot Cubs have won their last 7 games, taking the top spot from the Cardinals, who have lost their last four. The Brewers and Pirates are also very close, 1.5 and 3 games back respectively, and on 3 and 2-game win streaks respectively.
NL West
The Dodgers and Diamondbacks have revived a strong rivalry and have kindled a strong battle already, playing good baseball, with both teams winning 7 out of their last 10. Both clubs already have 20 wins and are only aiming for more. The Padres are also starting to show signs of improvement, but it is likely that the Dodgers and Diamondbacks will be the ones battling for their division.
AL East
Surprisingly, Tampa Bay continues their new success atop the AL East, two games over the Yankees. No one expected the Rays to jump out and lead the division, but they have started to maintain their success and seem to be here for real. Both the Yankees and the Red Sox are finally recovering after shockingly slow starts, 19-14 and 17-18 on the year respectively, good enough for 2nd and 3rd place in the division. If Tampa Bay can play well against the Red Sox and Yanks in their matchups, the Rays can distance themselves in the race.
AL Central
Another surprise, the Twins lead the AL Central by two games, over the Cleveland Indians, who many expected to lead the division this year. While the Indians are 18-14, their expected average factoring in Runs Scored and Runs Allowed should be 15-17, and every club in the AL Central has a negative run differential except the Indians, so it may be safe to say the Twins might be leading for a while.
AL West
In the AL West, the Astros have reclaimed the top spot and look to defend their title. The Mariners, whom no one expected to get to get off to the hot start that they enjoyed, have really fallen off and gotten themselves into a slump, dropping seven of their last 10 games to fall to a 19-17 record. The Astros will likely continue their success and stay atop the AL West